Currently, DNAs are used for personal authentication, for example, in criminal investigation or determination of parentage, utilizing characteristic portions of the DNAs having a high discrimination capacity. Recently, in addition to such applications, a method of judging the authenticity has been considered in which checks, bank bills, various certificates, cards, and the like are, for example, printed with an ink containing a DNA to address the forgery. For example, it is disclosed that a thin-film pattern is formed using a DNA ink for personal identification obtained by mixing a DNA molecule with a cationic surfactant, and the pattern formed is utilized as information for personal identification (see Patent Document 1). In this method, a complicated thin-film pattern formed by thin-filmy spread of the DNA molecule is optically detected as identification information, but characteristic biological information possessed by the DNA molecule is not utilized.
A method of judging the authenticity of a seal or handwriting is also disclosed in which a base sequence of a particular DNA fragment having a predetermined base sequence is used as an indicator (e.g., Patent Document 2). On the other hand, there exists a material which is obtained by incorporating a DNA into a gel substance or a microcapsule made of a plastic resin, for example, by interfacial polymerization, or a material which is obtained by previously binding a DNA onto a surface of an ultrafine particle made of a plastic resin and then mixing the resulting particle with an ink (Patent Documents 3 and 4).
All the above techniques using a DNA-containing ink differ from conventional authentication systems in respect of the use of a DNA, and are noteworthy. However, the DNA contained in the printed ink is often decomposed by an external stimulus such as light, an ultraviolet ray, heat, an acid, and an alkali. Accordingly, when a DNA is directly contained in an ink, the amount of DNA decreases immediately after printing and the detection becomes difficult. On the other hand, when a method of introducing a DNA into a microcapsule and the like or a method of retaining a DNA on a carrier such as a particle is used, the resistance to the external stimulus is improved. However, it takes a long time of one day or more to detect, for example, a DNA in an ink after printing as it is now.    Patent Document 1: JP-A-2002-167530    Patent Document 2: JP-A-2005-247900    Patent Document 3: JP-A-2004-175922    Patent Document 4: JP-A-2004-331832